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Living Fossils

The widespread extinction of many groups of organisms towards the end of the Permian is one of the great enigmas of the fossil record. This wave of mass extinction affected a variety of marine organisms including foraminiferida, tabulate and rugose corals, the trilobites, eurypterids and certain other arthropods, the goniatite cephalopods, productid and orthide brachiopods, and many groups of stalked echinoderms. On land the pelycosaur reptiles (paramam-mals) also became extinct. The demise of...

Marine animals with a lophophore (similar to the Bryozoa) protected by a bivalved shell. They are normally attached to the sea floor by a pedicle which emerges from the larger valve, but some brachiopods lose the pedicle and rest (on one valve) directly on the sea floor. Brachiopods use their lophophore to circulate water in the cavity between the valves, where they can extract organic matter in suspension or in solution. They have a free-swimming larval stage (of from one to twenty days) which...

Several widespread and fundamental changes in the composition of marine faunas occurred in the early Cenozoic. Many major components of Mesozoic communities disappeared, including ammonites, belemnites, inoceramid and rudist bivalves and many previously abundant gastropods including Nerinea and Actaeonella. Other forms such as trigoniid bivalves and the gastropod Pleuro-tomaria, common in Mesozoic shelf areas, became very restricted in distribution during the Tertiary Trigonia is now confined...

Throughout much of the Cretaceous, as in the Jurassic, the whole of Britain and much of western Europe fell within the Boreal Realm which was characterized by the rarity or absence of a number of major invertebrate groups including many important ammonite families, larger Foraminiferida and rudistid bivalves (Casey and Rawson, 1973 Hallam, 1973). The composition of tne faunas of the Boreal Realm was probably not controlled simply by temperature and salinity, but more likely by prevailing...

Communities comparable to those figured, together with many others not dealt with here, are found in the limestones which occur in all the regions of the Carboniferous equatorial belt. However, the taxa involved at any age vary in the different regions of the world. Broadly there are three main faunal realms 1 Eurasia stretching from China to Western Europe and including North Africa, the Middle East, and possibly Japan and Australia. Here the faunas of the Visean and Namurian are characterized...

With the development of stratigraphy, it has been found useful to develop a standard method of nomenclature. The Cambrian System consists of rocks deposited during the Cambrian Period. The system consists of rocks while the period is the time during which these rocks were formed. Both terms have an age connotation. Systems are recognized and defined by the fossils they contain. If the fossils within a system can be shown to change regularly with time, systems can be subdivided into series,...

Animals with a body composed of a head and or a foot, a visceral mass containing the internal organs, and a sheet of tissue (the mantle) which can secrete a calcareous shell. A space between the mantle and the visceral mass, known as the mantle cavity, contains gills and acts as a respiratory chamber. Most molluscs have a free-swimming larval stage. class MONOPLACOPHORA (Cambrian to Present) Mollusca with a single valve containing several paired muscle scars. Shallow marine benthos in the...

Animals with a notochord (a cylindrical sheath forming a flexible support for the back) or a backbone. Fish-like animals without bones or fins, but with a notochord (e.g. Amphioxus). subphylum UROCHORDATA (Permian to Present) The sea squirts or tunicates. Notochord only present in the larvae, which are active swimmers. Adults marine benthic or pelagic some colonial. subphylum VERTEBRATA (Ordovician to Present) Chordates with a skeleton of cartilage or bone. class AGNATHA (Ordovician to Permian...

A varied but small group, probably related to the Chordata, but without a notochord. Worm-like animals with no external skeleton. class PTEROBRANCHIA (Ordovician to Present) Fixed colonial organisms. Skeleton of protein. Lophophore attached by a stalk to an internal protein tube (the stolon). class GRAPTOLITHINA (Cambrian to Carboniferous) Colonial marine animals with a skeleton of protein. order Dendroidea (Cambrian to Carboniferous) Graptolites with a protein stolon, include benthic and...

In the Lower Jurassic, the marine benthos consisted mostly of invertebrates bivalves, gastropods and crustaceans are the commonest groups. These three groups all show major evolutionary advances when compared with their ancestors of the Palaeozoic. More bivalve taxa had developed siphons which enabled them Fig. n. Geography of the North Atlantic region during the Middle Jurassic Fig. n. Geography of the North Atlantic region during the Middle Jurassic to burrow more efficiently this was either...

Radioactive isotopes of rubidium and uranium decay slowly through time, and measurements of very small quantities of these isotopes show that some igneous rocks in western Greenland are about 3,800 million years old (Moorbath, 1975). These are the oldest dated rocks on the Earth's surface. Some inclusions in these very old rocks appear to have been derived from sedimentary rocks, suggesting that water has existed on the Earth's surface for more than 3,800 million years. Other isotopic work...

In addition to the above terms, which all have a time connotation, geologists have developed a hierarchy of rock-types (litho-stratigraphical) terms for bodies of rock which have distinctive characters, but which may not necessarily all be of the same age everywhere they occur. Groups, formations and members are the terms used. For example, the Swerford Member is a sand unit in the Chipping Norton Formation of Oxfordshire the Chipping Norton Formation is a unit of sands and limestones which...

A Protists with purely plant-like nutrition (photosynthesis) DIATOMACEA (Cretaceous to Present) Diatoms have brown protoplasm enclosed in a rigid silica skeleton. They occur as plankton and benthos in marine and fresh water. They are important primary producers of the marine food chain. B Protists with characters intermediate between animals and plants some are capable of swallowing solids, but most depend on photosynthesis capable of locomotion by means of flagella COCCOLITHOPHORIDA (Jurassic...

Fossils are the remains of plants and animals found buried in sedimentary rocks. To be preserved, an organism must leave some permanent record in the rock such as a shell, a burrow or some other impression. But it is also necessary for the sediment in which fossils occur to be preserved this can only happen by subsidence of the area where the sediment is deposited. The process of subsidence does not affect all habitats equally. In upland areas the remains of the inhabitants tend to have been...

The Ordovician period probably saw a greater expansion within the animal kingdom than any other similar time interval. The tri-lobites, which were the dominant marine animal group of the Cambrian, continued to diversify during the Ordovician but, in proportion to the other animals present, the trilobites no longer had their former dominance. However, new developments, like large raised eyes in phacopids and numerous long spines in odonto-pleurids, suggest that some trilobites spread out into...

Marine animals usually with a pentamerous symmetry, though some early forms have no radial symmetry, and some later echino-derms develop a superimposed bilateral symmetry. Skeleton composed of calcite plates. subphylum HOMALOZOA (Cambrian to Devonian) The carpoids echinoderms without radial symmetry. subphylum CRINOZOA (Cambrian to Present) Benthic echinoderms, with a clear pentamerous symmetry. This group includes the crinoids (which are usually attached by a stalk to the sea floor). Other...

Sponges consist of cells which are only poorly organized into tissues. Water is drawn through many small inlets on the surface of the sponge and ejected through fewer exits. Benthic, mostly in shallow marine environments, but some in deep water and a few in fresh water. The marine stromatoporoids Cambrian to Cretaceous , commonly thought to be coelenterates, might be included in the Porifera Hartman and Goreau, 1970 . Many so-called tabulate corals e.g. Chaetetes may also be sponges. class...

Southwards from Britain into western Europe, the faunal diversity gradually increased, particularly among the stenohaline groups of organisms. In France, ammonites and belemnites are found, accompanied by many other invertebrate genera seldom abundant in Britain. In general they occur in shallow water limestones with some sands and shales. In southern Europe Fig. n, p. 206 , however, the picture is totally different, fine grained pelagic facies being dominant and containing Radiolaria,...

All the Jurassic communities from Britain which have been described lived in the shallow sea which spread over parts of northwest Europe during the early Jurassic. In western North America, the Lower Jurassic commenced with a major phase of marine transgression and in general the western states California, Oregon and Nevada remained domin-antly marine. The seaway extended northwards through western Canada into southern Alaska and southwards into north-west Mexico Fig. m . Eastwards from Nevada...

Areas of Jurassic shelf often show sequences commencing with mud and passing upward through sandy mud and muddy sand and finishing with sand Communities 64 to 68 . If the water became very shallow at a distance from land i.e upon a shoal or 'swell' the currents carrying sediments were usually diverted to deeper parts of the sea. Little material was deposited on the sea floor in these shallow 'swell' areas except the remains of the animals and plants living there. Condensed limestones are...

Aquatic, terrestrial and aerial invertebrates, with a segmented body and jointed legs hence the name covered by chitin. Growth takes place through moults, so the chitin skeleton shows no growth lines. subphylum TRILOBITOMORPHA Cambrian to Permian In addition to the trilobites, this subphylum includes the class TRILOBITOIDEA, which are largely represented by fossils from the Middle Cambrian Burgess Shale of British Columbia. They appear to be a varied group, but to have similar appendages to...

Table VII Stratigraphical Nomenclature and correlation in the Carboniferous of Western Europe, U.S.S.R. and U.S.A. The Series names for Western Europe are those recognized by the International Subcommission on Carboniferous Stratigraphy. The Stage names for the Dinantian are those recently proposed by George et al. 1976 . Table VII Stratigraphical Nomenclature and correlation in the Carboniferous of Western Europe, U.S.S.R. and U.S.A. The Series names for Western Europe are those recognized by...

The infauna included specialized borers from many varied animal groups all of them were suspension feeders, each animal with its own particular form of boring. The bivalveLithophaga created a flask-shaped 'crypt' with a narrow entrance at the top it spent its whole life in the same place, gradually enlarging its crypt as it grew by secreting a chemical to dissolve the surrounding rock. Another bivalve Pholas had strong anterior ribs which ground the rock when the animal rotated. Some...

Modern communities contain a great variety of organisms which differ considerably in their preservation potential. Animals with well calcified rigid skeletons such as molluscs will obviously have the best chance of fossilization others such as echinoderms have well calcified skeletons, but are made up of very small pieces and are thus prone to disarticulation and dispersal. Many Crustacea have articulated and poorly calcified skeletons which cannot be easily preserved. Some of the most abundant...

Mucus-lined tubes in the soft sea bed, down which they suck detritus. Allen 1958 noted that modern lucinoids are able to live in environments with a low food content and with restricted supplies of oxygen, but that they cannot compete with other burrowing bivalves in more normal environments. The commonest suspension-feeding epifaunal elements are pectinids, bivalves which could keep their mantles free of mud by valve-clapping. The thin-shelled pectinids could create jet-propulsion by the same...

The marine faunas in the Silurian were dominated by benthic brachiopods and pelagic graptolites. Although trilobites occur in many environments, they were far less important than in the Or-dovician. Molluscs, bryozoans, ostracodes and crinoids are also present, but only common in some habitats. Towards the end of the Silurian, the land was just beginning to be colonized by plants, but animals with hard parts were absent from the land, although some arthropods and worms may have become...

During the Silurian, the same assemblages are present over North America, Europe and much of Asia. Shelf seas covered much of North America and the Russian platform including Gotland and many shallow marine areas were at great distances from the nearest land, so that no land-derived sediment was deposited. Instead, limestones, consisting of shells, corals and algal debris, accumulated through biological action. In these environments, the proportion of brachiopods and other invertebrates may be...

During the Miocene and most of the Pliocene, the shores of the North Sea Basin lay to the east of Britain, and marine deposition took place in northern Germany and Denmark. The shoreline advanced westwards again in the late Pliocene and early Pleistocene. From the Miocene onwards, marine faunas consist increasingly of extant species, including, in the north-west European deposits, species found today in the west Atlantic and the Mediterranean. The present day latitudinal sequence of faunas, or...

The late Middle Jurassic witnessed a phase of deepening seas accompanied by marine invasion of the earlier Middle Jurassic lagoons and deltas. The resulting environmental changes led to the deposition of more uniform marine sediments over much of northwestern Europe and provided sharp environmental contrasts with those that had preceded them. Although major marine invasion began in the late Middle Jurassic, as defined by ammonite zones, for convenience we have included these latest Middle...

Geography of North America and northern Europe during the Devonian modified after House, 1967 . The large land area is 'the Old Red Sandstone Continent' which formed after the closure of the Iapetus Ocean in the Late Silurian or Early Devonian. The Old Red Sandstone sediments were laid down in rivers and lakes, and yield freshwater fish and early land plants. were responsible for the construction of bioherms and other carbonate accumulations in many warm shallow-water environments...

Geography of the North Atlantic region during the Early Cretaceous Berriasian . Later in the Cretaceous the shelf seas became more extensive. After Hallam and Sellwood, 1976 . Fig. p. Geography of the North Atlantic region during the Early Cretaceous Berriasian . Later in the Cretaceous the shelf seas became more extensive. After Hallam and Sellwood, 1976 . or early Jurassic there was both a break-up of the North Atlantic continents and a rotation of the Iberian Peninsula, which caused...

E Lingulella Brachiopoda Inarticulata f Callograptus Hemichordata Dendroidea g Conotreta Brachiopoda Inarticulata e Lingulella Brachiopoda Inarticulata f Callograptus Hemichordata Dendroidea g Conotreta Brachiopoda Inarticulata Homalopteon, a nileid, is smooth and has much larger eyes than Asaphus or Ogygiocaris the smooth outline to the carapace may have been an adaptation for easier movement through the mud on the sea floor. The trinucleids have long genal spines extending back from the sides...

During the Permian and especially the early part of the period the seas withdrew from the continental masses, to a greater or less extent, in many parts of the world Fig. j . But some areas, including parts of Australia and the United States, contain marine sequences in which, in broad terms and with different taxa, many of the types of community seen in the Carboniferous persist. Permian marine onshore faunas, like those of the Carboniferous, are dominated by the brachiopods, which occupy...

Freshwater Middle Jurassic assemblages occur within the deltaic and lagoonal sequences as transported accumulates in marine and brackish water sediments. Characteristic Middle Jurassic freshwater mollusca included the turreted gastropod Bathonella Viviparus , the planospiral gastropod Valvata, and the bivalve Unio their descendants live in the same habitats today. The freshwater sediments are silty clays and sands which probably accumulated in rivers and low-lying lakes The sediments never...

Small colonial animals with a curved ridge bearing tentacles the lophophore which set up currents for feeding and respiration. The vast majority of the phylum the Ectoprocta have an external calcareous skeleton. subphylum ECTOPROCTA Ordovician to Present The skeleton may be encrusting for example on a molluscan or brachiopod shell , branching like a small coral , fan-shaped or nodular. Some ectoprocts contribute to reef formation. They are mostly sessile, usually on the sea floor, but some can...

The following account of Reef Communities Nos. 44 48 ofmid-Vis'ean Asbian age has been contributed by Mr. D. Mundy. Mid-Visean reef limestones are generally associated with a marginal situation between a stable shallow water 'shelf environment and a deeper subsiding'basin' environment, and are usually characterized by a marked contemporary topographic relief. This can take the form of discrete 'knolls' as in the 'Craven reef belt' or a continuous 'apron' as in north Derbyshire . In both cases...

This sediment consisted of finely broken shell debris which was the result of a combination of predation and mechanical erosion. It is likely that originally the sediment surface was rippled and provided a fairly mobile substrate. Thus, the fauna which inhabited it consisted of fairly specialized animals all adapted to withstand the somewhat rigorous environmental stresses. Many of the colonizing animals took refuge within the sediment and, consequently, many of the original sedimentary...

Six present communities are illustrated here four of these from around Britain and two from the tropical Indo-Pacific Province. The tropical communities are more diverse than comparable communities in higher latitudes Thorson, 1957 . The sands, sandy muds and muds in the shelf seas around the British Isles support a diversity of benthic communities, most of which became established after the beginning of the last major glacial advance about 15,000 years ago. The community illustrated is based...

Work on the distribution of Permian faunas and floras has suggested to several palaeontologists Stehli, 1971 Chaloner and Lacey, 1973 Yancey, 1975 that the variations found in the biotas from various parts of the world can be best explained by the existence of a marked thermal gradient between equatorial and polar regions. There were also geographical variations within the equatorial belt, as there were in the Carboniferous, enabling several faunal provinces to be distinguished. These are shown...

Animals with a nervous system often with stinging cells. The body has a single cavity with only one opening no separate anus . Free-swimming coelenterates medusoids have marginal tentacles ben-thic forms have tentacles round mouth on the upper surface, and usually have radial symmetry. Includes many soft-bodied forms e.g. jellyfish , but also the corals, which are important as fossils. class PROTOMEDUSAE Late Precambrian to Ordovician Jellyfish-shaped animals with radial lobes. Probably...

91 Lower Cretaceous Terrestrial Communities In parts of northern Europe the end of the Jurassic witnessed a phase of marked earth movements which caused some of the old subsiding marine basins to become swamps and marshlands. These early Cretaceous flood-plain regions were periodically inundated by seasonal rivers. In shallow pools along the watercourses and in the waterlogged parts of the flood plains horsetails Equisetales grew. One genus of this group of pteridophytes Equisetum still...

Cambrian time represents perhaps 80 million years, and is important as providing the first rocks containing abundant fossils of animals with hard parts see Precambrian chapter . However, few Cambrian fossil assemblages have been described from Britain and north-west Europe they are thus represented in this book by only four sea floor reconstructions designed to give a few glimpses of Cambrian life rather than to be a comprehensive sample. The Cambrian system takes its name from the Cambrian...

In many parts of the world the Carboniferous deposits preserve the record of a major transgression of the seas onto land areas, and the subsequent retreat of the seas to give continental or near-continental deposits in the upper part of the system. Palaeomagnetic evidence indicates that much of the United States, Europe and parts of Asia lay in the equatorial belt Fig. h and there is evidence of hot climates, including evaporite deposits, in these regions. Although the early Carboniferous...

The picture shows part of the reef top near its Iagoonal margin during the first Zechstein cycle at a later time than that shown in the previous picture. Laminated algal sheets bound and encompassed pockets of shell and bryozoan debris. On and between the upper surfaces of these sheets the benthos still included many brachiopods, but more bivalves and still more gastropods. All the species represented were survivors from the earlier reef but some of them had increased in numbers because rivals,...

108 Palaeocene Marine Sand Community The depositional environment of this community was an offshore shelf sea with a water depth of probably not more than 50m and a substrate of fine glauconitic sand. This sand community was dominated by infaunalbivalves various levels within the sediment were occupied by suspension feeding bivalves, while large, but fairly sluggish, Arctica morrisi was abundant near the surface of the sand and the patchily distributed small Corbula regulbiensis was buried...

Winson the authors are very grateful for the artistic skill, biological knowledge and patience she has shown in producing the drawing from our crude instructions, Mr P. Deussen drew the maps and other text-figures. We also owe thanks to Leslie and Tony Birks-Hay of Alphabet and Image who first suggested an illustrated book on fossils, and who guided us through many problems as the project developed. Specialist advice was generously given by the following Dr...

Table III The Silurian ecogroups and chief animal communities and their evolution with time Table III The Silurian ecogroups and chief animal communities and their evolution with time low. A few species change from one habitat to another with time, but the great majority of Silurian brachiopod lineages remain in the same habitat throughout the period. The succession of communities in one habitat with component genera changing through time must be distinguished from a single community where the...